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Cyclones hitting Australia plummet to 1500-year low

By Michael Slezak

OFF the chart&colon; cyclone activity in Australia has been lower over the last 40 years than at any time in the past 1500 years. The seemingly good news comes with a sting in the tail for people living on the coast.

The seemingly good news comes with a sting in the tail for people living on the coast

Radar and satellite records of tropical cyclones – rotating storm systems – stretch back only about four decades. For an idea of trends on the longer term, researchers must go underground.

Compared with typical monsoonal rains, the severe rains associated with tropical cyclones are unusually low in the heavier oxygen isotope – oxygen-18. Stalagmites forming in caves record this difference, so by analysing their growth bands – which form each year in the wet season – geologists can establish whether or not a given year was characterised by cyclone activity.

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Jordahna Haig and Jonathan Nott of James Cook University in Cairns, Queensland, Australia, and their colleagues examined stalagmites from the coast of Queensland and Western Australia. Their results show that cyclone activity in Australia since 1900 is dramatically lower than at any time since about AD 500. There was an even steeper drop from about 1960, corresponding closely with the sharp increase in global temperatures (Nature, DOI&colon; 10.1038/nature12882).

Climate models predict that cyclone frequency will decrease – and individual cyclones will become more intense – as the world warms. However, these effects were only expected to be significant by about 2050. “What we’re saying is that we’re seeing this now,” says Nott.

That’s bad news for people living on Australia’s coast, because it suggests that the infrequent cyclones they experience will be more intense, with stronger storm surges and more flooding than past cyclones. “We’ve grossly underestimated the risks with building close to sea level,” says Nott.

This article appeared in print under the headline “Cyclone action in Australia hits 1500-year low”